The present invention relates to an image processing apparatus and method, more particularly, to an image processing apparatus and method which control levels of input image signals so as to be suitable for a destination device to which the image signals are transmitted.
An image forming apparatus, such as a color copying machine, can be used as an apparatus for visualizing and outputting a color image generated by an external device, such as a computer.
FIG. 1 is a block diagram illustrating a configuration of a color copying machine 100. In a normal copying operation, a reader 101 reads an original image, an image processing unit 107 processes image signals of the original image, then obtained C, M, Y and K image signals are outputted to a printer 105 where an image is formed. In addition, C, M, Y and K image signals generated by an external device 106 are directly inputted to the printer 105 of the color copying machine 100, and an image is formed. The latter image forming method requires a relatively simple configuration, however, there are the following undesirable problems.
In a case where the printer 105 uses a color electrophotographic method using toners, there is a limitation in the total amount of toners which forms one dot on a recording paper sheet, or in the sum of the C, M, Y and K signal values, depending upon the capability of a printer. For example, when an eight-bit signal value representing each of C, M, Y and K signals is used, the quality of the output image is guaranteed up to the sum of the C, M, Y and K signal values less than 690, however, if the sum exceeds 690, the quality of the image is beyond guarantee. In a case where the C, M, Y and K signals inputted from the external device 106 are directly sent to the printer 105, and each of C, M, Y and K signals has the maximum value (255), the sum of the signal values becomes 1020 which far exceeds 690. Thus, when the C, M, Y and K signals whose total value exceeds the capability of the printer 105 are inputted, a deteriorated image is outputted because of dispersion of toners caused by transfer error and fixing error.
Note, in the following explanation, the sum of the C, M, Y and K signal values which indicates the maximum amount of toners that can form one dot on a recording paper sheet depending upon the capability of a printer may be called the "maximum input level" of a printer.
Further, when input image signal levels are controlled based on a destination device, a color image may be outputted in colors which a user does not desire as the controlled result.